TOWARDS A PHILOSOPHY OF COMPUTER SCIENCE

SCIENTIFIC CARSIt has been identified that there is a small risk of a brake problem in certain Scientific models. While customer safety has always been the primary focus for Scientific, we never intended the handbook to be a description of how the brakes should behave but rather as a theory or prediction of their behaviour. In keeping with this, we encourage drivers to test their brakes under the most extreme circumstances. We understand that that this might cause nightmares among the infirm, but Scientific would greatly appreciate receiving details of the resulting information. At no time shall we recall cars that are unsafe, but be assured that, in the fullness of time, we shall issue new handbooks that provide a better theory of how the breaks will perform.

1SPECIFICATION and ARTEFACT22OutlineSpecifying ArtefactsThe Varieties of SpecificationDefinitionsPhysical ArtefactsAbstract ArtefactsTheory and Specification

33SPECIFYING ARTEFACTS4Why Specification?The specification and construction of computational artefacts is a central activity of Computer Science.This stretches beyond software engineering. As an activity it is to be found throughout the discipline. Indeed, it is partly constitutive of it.Unpacking the nature of specification will provide some conceptual insight into the nature of CS.

5Computational Artefacts Much of computer science involves the design, specification, analysis and implementation of computational artefacts

ProgramsAlgorithmsProgramming LanguagesDatabasesCompilers and InterpretersOperating SystemsMachinesType Inference SystemsTheorem proversSystems on a chipNatural Language systems of various kindsSpeech recognitionVisual processing systemsComputer games...

6The Role of SpecificationTo describe the artefact not how to build itIn software development, a functional specification describes the behaviour of a computer program or larger software system. Knowing what versus knowing how (to Build).More information about implementation provides more knowing how.Different levels of both for users and designers

7 In some paradigms specifications also have a more controversial role which is to guide the actual process of artefact construction.To inform the discussion we need some examples.

7VARIETIES OF SPECIFICATION88TECHNICAL SPECIFICATION STEAM AND WATER SAMPLING SYSTEM FOSSIL POWER PLANTPrimary coolers and cooling water system. Sample temperature shall be reduced using full counterflow sample coolers to achieve a temperature within 50 F of the temperature of the primary cooling water. All coolers are furnished as an integral part of the conditioning rack. Certified performance data on all coolers shall be provided at design conditions. All coolers shall be of the coil in shell design, with counterflow of sample and cooling water. Coolers shall be Sentry type TLF, FLF or FXF, with a single flange and gasket shell design. For maintenance, the sample coolers shall have removable shells. All coolers shall have 316 stainless steel tubing and 304 stainless steel shells. All coolers shall be arranged side by side in the rack, and shall be connected to an inlet and an outlet cooling water header. Coolers shall be located for easy access to the throttling valves and for simplified maintenance and replacement, as necessary. In addition, cooling water piping shall not disturb the sample piping. Sample piping shall not interfere with the removal and replacement of the cooler coils and/or shells. All coolers shall be equipped with outlet globe valves for throttling the flow of cooling water, and a 3-way ball valve on the inlet. Cooling water headers shall be of carbon steel and of the appropriate size to handle the required flow rate to the coolers. The inlet cooling water header shall be equipped with a relief valve sized to adequately relieve excess cooling water pressure. Outlet cooling water headers shall include a vent for air removal, as required.9ArithmeticP[x, y] z. y=x+zG(x) 3x+2x+7x+9F(0) 12 F(n+1) 3F(n) + 8a x.xNx